1. Field of the Invention
The invention relates to a rear wheel steering system that is applicable to a four-wheel steering vehicle of which the front wheels and the rear wheels are both able to be steered.
2. Description of Related Art
There is a four-wheel steering vehicle of which the front wheels and the rear wheels are both able to be steered. When the four-wheel steering vehicle is traveling at a low speed, for example, when the vehicle is being parked, the rear wheels in addition to the front wheels are steered and thus the vehicle is able to turn in a small radius. Thus, for example, during parallel parking, the direction in which a steering wheel is rotated need not be changed so many times. There is a rear wheel steering system that steers the rear wheels in such a four-wheel steering vehicle (see Japanese Patent Application Publication No. 2006-035917 (JP 2006-035917A)).
JP 2006-035917A describes an example of a four-wheel steering vehicle. Specifically, a pair of right and left knuckle shafts, to which respective rear wheels are fitted, are fitted to a rear portion of a vehicle body such that the knuckle shafts are able to be steered. The knuckle shafts are coupled to each other via a tie rod respectively. In addition, piston rods of steering cylinders fitted to the vehicle body are coupled to the respective knuckle shafts, and the knuckle shafts are steered together with the rear wheels based on the strokes of the piston rods. In the four-wheel steering vehicle described in JP 2006-035917A, the knuckle shafts, the tie rods and the steering cylinders constitute the rear wheel steering system.
When the four-wheel steering vehicle is travelling at a high speed, it is desirable that steering of the rear wheels be locked in a neutral state where the steered angle of the rear wheels is zero, in order to stabilize the vehicle body. However, steering of the rear wheels may be locked in a state where the steered angle of the rear wheels has not been completely returned to zero due to an unexpected trouble, or the like. In such a case, it is desirable that the rear wheels should be returned to the neutral state after steering of the rear wheels is locked.